Buggy code:
GridData gd ; gd = new GridData ( ) ; gd . grabExcessHorizontalSpace = true ; gd . grabExcessVerticalSpace = true ; gd . horizontalAlignment = GridData . FILL ; gd . verticalAlignment = GridData . FILL ; this . vexWidget = new VexWidget ( this . parentControl , SWT . V_SCROLL ) ; gd = new GridData ( ) ; gd . grabExcessHorizontalSpace = true ; gd . grabExcessVerticalSpace = true ; gd . horizontalAlignment = GridData . FILL ; gd . verticalAlignment = GridData . FILL ; this . vexWidget . setLayoutData ( gd ) ; VexActionBarContributor contributor = ( ( VexActionBarContributor ) ( this . getEditorSite ( ) . getActionBarContributor ( ) ) ) ; MenuManager menuMgr = contributor . getContextMenuManager ( ) ; this . getSite ( ) . registerContextMenu ( menuMgr , this . vexWidget ) ; this . vexWidget . setMenu ( menuMgr . createContextMenu ( this . vexWidget ) ) ; this . savedUndoDepth = this . vexWidget . getUndoDepth ( ) ; IContextService cs = ( ( IContextService ) ( this . getSite ( ) . getService ( IContextService . class ) ) ) ; cs . activateContext ( "org.eclipse.wst.xml.vex.ui.VexEditorContext" ) ; IHandlerService hs = ( ( IHandlerService ) ( this . getSite ( ) . getService ( IHandlerService . class ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.ChangeElementAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new ChangeElementAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.DeleteColumnAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new DeleteColumnAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.DeleteRowAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new DeleteRowAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.DuplicateSelectionAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new DuplicateSelectionAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.InsertColumnAfterAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new InsertColumnAfterAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.InsertColumnBeforeAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new InsertColumnBeforeAction ( ) ) ) ) ; <START_BUG> hs . activateHandler ( "net.sf.vex.editor.action.InsertElementAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new InsertElementAction ( ) ) ) ) ; <END_BUG> hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.InsertRowAboveAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new InsertRowAboveAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.InsertRowBelowAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new InsertRowBelowAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.MoveColumnLeftAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new MoveColumnLeftAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.MoveColumnRightAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new MoveColumnRightAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.MoveRowDownAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new MoveRowDownAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.MoveRowUpAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new MoveRowUpAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.NextTableCellAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new NextTableCellAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.PasteTextAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new PasteTextAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.PreviousTableCellAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new PreviousTableCellAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.RemoveElementAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new RemoveElementAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.RestoreLastSelectionAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new RestoreLastSelectionAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.SplitAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new SplitAction ( ) ) ) ) ; hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.action.SplitItemAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new SplitItemAction ( ) ) ) ) ; this . vexWidget . addSelectionChangedListener ( this . selectionProvider ) ;

Fix:
hs . activateHandler ( "org.eclipse.wst.xml.vex.ui.editor.action.InsertElementAction" , new ActionHandler ( new org . eclipse . wst . xml . vex . ui . internal . action . VexActionAdapter ( this , new InsertElementAction ( ) ) ) ) ;